1. Field of the Invention
The present invention relates to permanent isolation seals for mining applications and, more particularly, to a permanent seal in an underground entry to isolate the atmosphere on one side of the seal from the atmosphere on the other side.
2. Description of Related Art
In underground mining, there is typically a need to isolate the atmosphere in a specific portion of the mine. A seal is provided to isolate areas of the mine for purposes such as to limit the area of the mine workings that need to be ventilated, to control the dissemination of any toxic or explosive gases in the mine, or to allow the atmosphere in an isolated part of the mine to change its composition to a less hazardous state. Seals are constructed across individual mining entries or tunnels to provide such isolation.
Seals have been traditionally constructed as walls of stacked concrete blocks that may be coated or joined together with a cementitious material, which is considerably weaker than the concrete blocks themselves. Further, the cementitious material typically shrinks over time creating leaks in the seal and possibly allowing dangerous gases to bypass the seal. Blocks are fitted across a mine opening in a staggered or overlapping relationship. Such seals, however, have not been found to withstand mine explosion overpressures of over 20 psi. More recently, a mine seal has been employed that incorporates concrete block walls sandwiching an inner core of a polymeric material containing aggregate. This composite structure of a core provided between two concrete block walls (described in U.S. Pat. No. 5,385,504, incorporated herein by reference), is constructed by dry-stacking concrete blocks to form walls between the roof, floor and ribs of a mine entry. A rear wall is first constructed and wedged into place. Next, a front wall is constructed to a height of 2-3 feet and construction continues by pyramiding the blocks until one or two blocks are in contact with the roof. The core material is installed between the fully constructed rear wall and the partially constructed front wall by providing a layer of aggregate material (gravel or the like) between the walls and coating the aggregate material with foamable polyurethane. As the polyurethane foams and cures, the polyurethane increases in height (with the aggregate mixed therein) and solidifies, adhering to the rear and front walls. Construction of the front wall continues and additional layers of the core material (polyurethane and aggregate) are provided between the rear wall and the growing front wall until the core material and the front wall reach the roof of the mine entry. The outside surface of the front wall is covered with a coating of a fire-resistant sealant satisfying the guidelines of the Mine Safety and Health Administration (MSHA). While this composite seal withstands mine explosion overpressures of at least 20 psi, a need has been identified to increase the pressure rating of mine seals.